Environmental officials are testing the water for pesticides and oxygen levels for possible clues. As a precaution, they’re warning consumers to only buy seafood from authorized vendors.

“Dead fish found on shore should not be collected by general public,” the Fisheries and Oceans department tweeted. “Consumers should only purchase from licensed harvesters/sellers.”

According to the US Geological Survey, a number of factors could contribute to fish kills.

While toxic chemical exposure can be one cause, most fish kills are attributed to low concentrations of dissolved oxygen in the water, according to the USGS.

Just this year, mass fish deaths were reported in Florida’s Indian River Lagoon and Hongcheng Lake in Haikou, China.

In Florida, dead fish blanketed the Atlantic coast for miles in March. The deaths were caused by a combination of environmental factors. Warmer waters, increased precipitation and pollutant runoff made way for toxic algae blooms and brown tide, ultimately depleting the water of oxygen.

In China, an estimated 35 tons of fish died at Hongcheng Lake in May. While residents blamed the fish kill on pollution, local authorities attributed the incident to changes in salt levels.